1. Field of the Invention
The present invention concerns the use of guluronic acid-rich alginates or galacturonic acid-rich pectins, so-called G-block polysaccharides, as modulator for the rheology in a mixture in which a gelling, water-soluble polysaccharide is a component which is intended to give the final product a changed viscosity, stability, elasticity, rigidity or similar.
Alginates are isolated from marine brown algae. Alginate is also produced in soil bacteria such as Azotobacter vinelandii and Azotobacter crococcum and many different Pseudomonas bacteria, but the commercially available alginate stems mainly from brown algae.
Pectins can be isolated from many different sources as it is found in the cell walls of fruit and vegetables, but the commercially available pectins are usually isolated from apples or citrus fruits.
These polysaccharides, alginate and pectin, are used in foods and in pharmaceutical, dental, cosmetic and other industrial products. The most common industrial uses are based on their hydrocolloid and polyelectrolytic nature, which forms the basis for the gelling, thickening, stabilising, swelling and viscosity-producing properties.
In foods such as jam, ice cream, packet soups and sauces, polysaccharides have a thickening, stabilising effect. In mayonnaises and dressings, they also act as an emulsion stabiliser.
In products such as baking creams and tinned pet food, the ability of alginate to form thermally stable gels, which are produced and hardened at room temperature, is used.
There is also great potential for the use of alginate in biotechnological and medical applications. Examples of this are the mass production of alginate-based solid nutrient medium for plant tissue cultures, alginate as an administration medium with slow release of a drug and encapsulation of live insulin-producing cells in alginate gel for implantation in patients.
Alginates are salts of alginic acid, a linear heteropolysaccharide consisting of (1xe2x86x924) linked xcex2-D-mannuronic acid, designated M, and xcex1-L-guluronic acid, designated G. These two uronic acids have the following formulae: 
The polymers exist as homopolymer sequences of mannuronic acid, called M blocks, homopolymer guluronic acid sequences, called G blocks, and mixed sequences of mannuronic acid and guluronic acid units, so-called MG blocks or alternating blocks.
In order to illustrate the structure of the alginates, we show a schematic representation of a possible block structure. 
Usually, alginate contains all three types of blocks and a block generally consists of three to thirty monomer units. The distribution of blocks depends on the type of algae from which the alginate is isolated as well as the age and part of the plant, for example alginate from the stem may have a different sequence and block composition to alginate isolated from the leaves. The season in which the algae are harvested also affects the block composition and sequence. On the basis of our present knowledge, the maximum G content in the stem is to be found in old L. hyperborea. Leaves from the same species have a somewhat lower G content and shorter G blocks, but the content is still higher than in most other species. The commercially available alginates usually have a G content of 25%-70%. Pectin has a complex structure with a polysaccharide chain in which xe2x80x9csmoothxe2x80x9d and xe2x80x9chairyxe2x80x9d regions alternate. The smooth regions consist of non-dendritic (1xe2x86x924) inked xcex1-D-galacturonic acid with the following formula: 
with some (1xe2x86x922) linked L-rhamnose, while the hairy regions are very dendritic and consist mainly of (1xe2x86x923) and (1xe2x86x926) linked xcex2-D-galactose, (1xe2x86x923) linked arabinose and some (1xe2x86x923) linked xylose. The galacturonic acid groups are partially methoxylated.
In the following xcex1-D-galacturonic acids are designated G units, and the regions which mainly consist of such G units are designated G blocks. Thus guluronic acid blocks from alginate and galacturonic acid blocks from pectin come under this common designation in the following.
Below we show a schematic representation of a possible pectin structure: 
Alkali metal salts, magnesium salts and ammonium salts of alginates and pectins are water-soluble. By adding multivalent cations, for example multivalent ions such as Ca2+, Sr2+, Ba2+, Fe3+or Al3+ions, to a polysaccharide solution, a gel is formed as a result of the production of ionic cross-links of several polysaccharide chains. The G units are responsible for the ability of these polysaccharides to link multivalent cations and this leads to the G blocks functioning as bindingseats between the various polysaccharide chains in connection with gelling.
The gel strength of polysaccharide gels will depend on various parameters such as the G content of the alginate or pectin, the length of the G blocks, the calcium activity and the molecular weight and concentration of the polysaccharides.
2. Description of the Related Art
Reference is made to xe2x80x9cFood Polysaccharides and their applicationsxe2x80x9d, Ed. Alistair M. Stephen, [1995] Chap. 9: xe2x80x9cAlginatesxe2x80x9d, S. T. Moe, K. I. Draget, G. Skjxc3xa5k-Brxc3xa6k and O. Smidsrxc3x8d, pp. 245-286, and Chap. 10: xe2x80x9cPectinsxe2x80x9d, A. G. J. Voragen, W. Pilnik, J. F. Thibault, M. A. V. Axelos and C. M. G. C. Renard, pp. 287-339.
These overview articles are to be considered to be included in their entirety.
If you react a water-soluble polysaccharide in solution with an easily soluble Ca salt, you will get an undesirable, lumpy consistency of gel or gel balls, depending on the procedure. In the preparation of continuous gels, it has, therefore, been common to use either dialysis or in situ gelling methods.
In dialysis, the cross-linking ion, usually calcium, diffuses into the polysaccharide solution and this then produces a continuous, inhomogeneous gel which is strongest near the diffusion surface.
In in situ gelling, the calcium ions are released inside the polysaccharide solution. An inactive form of calcium has been used together with an agent which makes possible a slow release of the ion, which produces a homogeneous gel and the gelling speed can be controlled. It has been common to use sequestering agents such as citrate, phosphate or EDTA to achieve controlled release of the cross-linking ion.
Alternatively, insoluble salts or salts which are hard to dissolve such as calcium sulphate or calcium carbonate have been used. In connection with the addition of an agent which makes possible a slow release of protons and thus a slow release of calcium ions, the gelling speed can be controlled. An example of such an agent is D-glucono-xcex4-lactone (GDL).
Another possibility, which is used in tooth filling masses, is to replace the lactone with a system consisting of acid, base and a buffer. The buffer (Na4P2O7) reduces the gelling speed by initially linking the calcium ions which are released from the calcium sulphate. This produces a self-gelling system in which the gelling is started when water is added at the user""s premises.
From U.S. Pat. Nos. 2,441,720 and 2,918,375 (Kelco Company), a procedure is known for the production of alginate gel in which a water-soluble alginate salt (usually potassium or sodium alginate) is converted with a calcium salt which is hard to dissolve such as tricalcium phosphate or calcium tartrate. In these systems, the calcium ions are released by means of acid or acidifying agents. The reaction speed of the reaction between the calcium ion and the water-soluble alginate is controlled by means of a gel-delaying or gel-inhibiting agent such as sodium hexametaphosphate.
In U.S. Pat. No. 3,060,032 (General Foods Corp.), calcium alginate gel is used to improve the freeze-thaw stability in frozen dessert jellies. This calcium alginate gel is produced from sodium alginate, calcium tartrate and sodium hexametaphosphate. The reaction speed of the reaction between the calcium ions, which are released from the tartrate, and the sodium alginate is controlled by means of the sodium hexametaphosphate.
The use of calcium alginate gel in thermally stable baking creams is known from U.S. Pat. No. 3,352,688 (Kelco). This system consists essentially of sodium alginate, dicalcium phosphate and sodium hexametaphosphate.
In U.S. Pat. No. 3,770,462 (Kelco), the use of sodium phosphor alginate and calcium sulphate dihydrate is described for the production of milk puddings of type vanilla pudding. In this case, the alginate and calcium sequestering agent are mixed carefully during the production of the sodium phosphor alginate from alginic acid. This makes possible the hydration of the alginate in cold milk because the milk calcium is sequestered by the phosphate in the alginate. The calcium which is released from the calcium sulphate dihydrate reacts with the soluble alginate so that a homogeneous calcium alginate gel is formed.
U.S. Pat. No. 2,809,893 describes a dry powder mixture for forming gels for use in desserts. Such gels contain sugar, alginate, sodium hexametaphosphate, sodium citrate, citric acid, heat-treated water-free monocalcium phosphate and various taste enhancers and colorants.
EP345886B1 describes an alginate gelling system for meat products in which the release of calcium and thus the gelling speed are controlled by means of encapsulated calcium salts. All commonly used calcium salts approved for use in food products can be used and the examples stated include calcium chloride dihydrate, calcium lactate pentahydrate, calcium acetate, calcium malate and calcium gluconate. The calcium salts are encapsulated in a fat derivative which may be a fatty acid, a glyceride and preferably also a hardened vegetable oil.
U.S. Pat. No. 5,503,771 describes a gelling suspension which contains colloidal metal particles or ceramic particles, water and an effective quantity of a biopolymer dispersant with a molar weight of at least 1000 to 5000 g/mol, as well as a biopolymer gelling agent which has a molar weight of at least 50,000 g/mol and which can be converted from a non-gelled state to a gelled state. The biopolymer dispersant may be chosen from, among others, a group consisting of a polymannuronic acid-rich hydrolysis product of alginate, a polyguluronic acid-rich hydrolysis product of an alginate, poly-D-glutamic acid, poly-L-glutamic acid, poly-DL-aspartic acid, pectin and mixtures of these. The biopolymer gelling agent can be chosen from a group consisting of gelling polysaccharides, polypeptides, proteins or nucleic acids. Alginates with molar weights in the order of 75,000 to 100,000 g/mol or higher are stated as possible polysaccharides, among others. The biopolymer dispersant is to disperse the colloidal particles in water and thus contribute to the formation of a non-aggregated suspension which has a low, pourable viscosity so that the final suspension can be transferred to a casting mould before gelling is started, after which the product is pyrolysed and sintered. The main intention is to achieve a dispersed product in which the gelling keeps the dispersed particles in place. There is no description whatsoever concerning the use of this combination of alginate and polyguluronic acid-rich hydrolysis product of alginate as a modulator for rheology. On the contrary, as both polymannuron-rich hydrolysates and polyguluron-rich hydrolysates of alginate can be used with no difference as the dispersant in combination with alginate as the gelling agent, this US patent concerns a different procedure to that of the present invention.
In order to be able to utilise the valuable properties of polysaccharides as gelling and film-forming agents, viscosity producers and stabilisers of emulsions and suspensions in various types of products, it is of decisive importance to control the parameters such as gelling kinetics (for example, absorption of cross-linking ions), gel strength and syneresis, i.e. the rheological properties. This applies to foods but also to other products such as the use of alginate as a thickener for paint paste for textile printing.
In the prior art, the gelling technique is controlled by using both calcium salts which are hard to dissolve such as phosphates, sulphates, citrates or tartrates and sequestering agents, which are very often phosphates, as well as possibly other acids or buffers.
In particular, the addition of phosphate, which has reached a high level in foods in the industrialised parts of the world, seems to be problematic because a high intake of phosphate disturbs the ion equilibrium in the body and this can have unfortunate health-related consequences. In addition, phosphates and the other additives may produce undesired effects such as poor taste and a different consistency to that desired. This applies, for example, to the production of restructured meat products and baking creams.
Against this background, there is, therefore, a need for a system which can utilise the valuable properties of polysaccharides in a controlled manner without having to use many additives or such large quantities of additives, in particular a system which avoids or reduces the use of phosphate.
In dairy products, i.e. milk-based products, it is desirable to produce various effects from polysaccharide, for example in some products only a thickening effect is required, as in yoghurt, while in other cases, a strong gel is required, as in the production of pudding. As there are large quantities of calcium in milk and the calcium content affects the parameters such as gel strength and syneresis, there are problems in connection with obtaining products of t he desired consistency and stability. If the end products are too exposed to syneresis, i.e. a contraction of the gel during the expulsion of liquid, the quality is seriously reduced and the durability curtailed.
Regarding the use of alginate in paint paste used in textile printing, the thickening and shear thinning properties are used. In areas where there is hard water, i.e. where the calcium content of the water is high, local gel particles are produced (so-called xe2x80x9cfish eyesxe2x80x9d). In order to avoid this, sequestering agents, usually phosphates, a re added. These agents later constitute an environmental problem as they are washed out and end up in drainage water, from which they must be removed.
There is, therefore, also a need for a system which can utilise the valuable properties of polysaccharides within such areas of application in which the presence of natural, i.e. not added calcium, constitutes a problem. This requires a system in which the rheological properties of alginates or pectins can be controlled when the substances are used as thickeners, gelling agents, binders or stabilisers.
According to the present invention, it has now, surprisingly, been found that xe2x80x9cG-block polysaccharidesxe2x80x9d can be used as modulators for rheology in gelling polysaccharide systems within various areas of application. This means that xe2x80x9cG-block polysaccharidesxe2x80x9d, i.e. blocks of guluronic acid from alginate or blocks of galacturonic acid from pectin, make it possible, in an alginate and/or pectin system, to control the gelling kinetics, gel strength, viscosity, elasticity, equilibrium properties and syneresis.